Permanent waving of hair is accomplished by first arranging the hair in the desired configuration and applying a chemical which breaks the cystine sulfur to sulfur bonds found in the hair fibers. A second chemical, referred to as a neutralizer, is then applied to reform the sulfur to sulfur bonds. The resulting hair has become permanently waved.
Chemicals which are capable of breaking cystine sulfur to sulfur bonds are referred to as reducing agents. A wide variety of reducing agents exist; some of the more popular ones include thio compounds, sulfites and cysteine or cysteamine derivatives. Permanent waving can be carried out at either acid or alkaline pH, depending on the particular reducing agent selected. For example, acid permanent waves utilize reducing agents which are capable of curling hair at a pH of less than or equal to 7.0. These reducing agents generally have a low pKa value and exist predominantly in the dissociated form at a pH at or near neutral. On the other hand, alkaline permanent waves use reducing agents which have pKa values which are higher. For example, ammonium thioglycolate has a pKa of 10.4, thus it is effective as a waving agent only if the pH of the entire system is exceeds 9. Generally, the pKa of a reducing agent dictates the pH at which permanent waving must take place. If the pKa of a reducing agent is greater than 7.0, permanent waving efficiently takes place only at alkaline pH. Conversely, if the pKa of a reducing agent is less than 7.0, effective permanent waving only takes place at pH values less than or equal to 7.0.
It is well known that cysteamine or salts thereof are suitable reducing agents for permanent waving. The pKa of cysteamine is 9.0, meaning that it is most effective in breaking sulfur to sulfur bonds at alkaline pH. Cysteamine is generally used in conjunction with other reducing agents, such as thio compounds, because it is expensive and it is believed that the combination of cysteamine and thio compounds provides a synergistic effect. However, U.S. Pat. No. 5,260,054 teaches a permanent wave composition where cysteamine can be used alone as the sole reducing agent provided the pH of the composition falls within the narrow range of 7.8 to 8.8 and the cysteamine concentration of the composition ranges from 7.8 to 9.0 wt %. The '054 patent teaches that below pH 7.8 cysteamine performance is not adequate to permanent wave hair, and above a concentration of 9.0 wt % cysteamine, the product is too irritating to skin.
Applicants have most unexpectedly discovered that cysteamine based permanent waving can be very effectively accomplished at a pH range of 6.0 to 7.0 (far below the pKa of cysteamine), with compositions containing 10-20%, preferably 12-18% by weight cysteamine reducing agent. The compositions provide no discomfort or irritation, and more effectively permanent wave the hair than at alkaline pH and with lower concentrations of cysteamine.